(a) Field of the Invention
This invention relates to the recovery of oil from subterranean heterogeneous petroleum-bearing reservoirs, and more particularly to such recovery by an enhanced oil recovery process involving plugging the higher permeability channels of the reservoir, injecting a micellar solution, and injecting a drive fluid.
(B) Description of the Prior Art
It has long been recognized that substantial amounts of oil remain unrecovered at the completion of normal primary recovery operations. This is especially true of reservoirs having heterogeneous permeability. Hence, various secondary and tertiary methods of recovering additional quantities of oil have been developed, such as methods involving the injection via one or more injection wells of a micellar solution to drive additional oil toward one or more production wells spaced apart in the reservoir from the injection well. The micellar solution can be followed by a drive fluid. Heterogeneity in the reservoir structure often results in the injected fluid not being uniformly distributed throughout that portion of the reservoir being treated. Thus, various processes have developed for improving the volumetric sweep efficiency of injected enhanced recovery fluids. U.S. Pat. No. 3,882,938 to Bernard describes such a process wherein there is sequentially injected into a heterogeneous reservoir; (a) a first portion of a soluble oil solution, (b) one or more aqueous solutions of reagents that react together in the reservoir to form a plugging material that reduces the permeability of the more permeable strata of the reservoir, (c) a second portion of the soluble oil solution, and (d) an aqueous drive fluid. It has been found that some of the plug-forming reagents have a tendency to react with the surface active agent component of the soluble oil solution to form a polyvalent metal salt. The soluble oil is then less effective in lowering the surface tension between the reservoir oil and the subsequently injected aqueous drive fluid. Thus, less oil will be mobilized in the reservoir during the recovery process.
Accordingly, a principal object of this invention is to provide an improved enhanced oil recovery process for reservoirs having heterogeneous permeability.
Another object of this invention is to provide such a process involving the use of a micellar solution.
Still another object of this invention is to provide such a process for increasing the volumetric sweep efficiency of a small amount of a micellar solution injected ahead of a drive fluid.
A further object of this invention is to provide such a process wherein the efficiency of the micellar solution for sweeping oil from the reservoir is maintained.
Other objects, advantages and features of this invention will be apparent from the following detailed description: